1. Field of the Invention
The invention relates to an operating method for an apparatus, having an internal combustion engine that can be operated in a lean mode and a stoichiometric mode. In addition a crankcase, at least one combustion chamber and preferably a throttle element, via which charge air can be fed from a charge air cooler to the combustion chamber, are provided.
2. Description of the Related Art
In gas engines, unexpectedly high emissions of fine dust particles occur, which is noticeable in the form of a high particle count in the approval cycle, which is prescribed for EURO VI engines, WHTC (World Harmonized Transient Cycle). The particle emission is not increased over the entire 30-minute cycle but instead is manifest in very high emission peaks, in particular after idling phases.
The mechanism by which it occurs is explained as follows:
Owing to the spark-ignition-engine combustion process, a throttle valve via which charge air can be fed from a charge air cooler to an internal combustion engine is closed during idling, with the exception of a small gap. An underpressure with respect to the surroundings is produced in the intake manifold. During the intake stroke, an underpressure is also produced in the combustion chamber of the engine, for which reason an underpressure with respect to the crankcase of the engine also occurs in the combustion chamber. As a result, air from the crankcase is drawn into the combustion chamber (Reverse-Blow-By). As a result of the movement of air, engine oil is conveyed from the area of the cylinder liner/piston into the combustion chamber. As a result of the low intensity of the combustion during idling, the oil collects in the combustion chamber. If an increase in load takes place after a relatively long idling phase, the collected oil is burnt within a short time period due to the increased flame intensity. High emissions of particles come about as a result of unburnt oil residues (oil ash). This effect is increased because the quantity of oil in the combustion chamber is not taken into account in the metering of fuel. A deficiency of oxygen is present in the combustion chamber, which promotes the emission of particles.